Immersion lithography was so quickly adopted because it was based on the
proven principles of immersion microscopy that stretched back to the
1600s when the English natural philosopher Robert Hooke predicted it. In
the 1800s it was demonstrated by Giovanni Battista Amici an Italian
astronomer and microscopist. And in the 1900s it was perfected to a
science for microscopy.

The principle is that light bends at the
interface to a liquid medium--the imitable bend stick in a glass of
water--thus magnifying a microscope's image as it comes up through an
immersed lens. Likewise, when light passes down through a lithographic
reduction lens immersed in a liquid, it shrinks an image by its
index-of-refraction. Today we know that combining immersion lithography
with multiple-patterning--splitting up a mask into parts that can be
exposed in separate steps--the resolution of standard 193-nanometer
lithography can be extended to 32-nanometer. And with more sophisticated
multiple patterning, and higher index fluids, 193-nanomoter lithography
could go all the way down.

"Intel has already achieved the
32-nanometer node with triple-patterning, and many engineers are talking
about making it all the way to 14-nanometer with multiple patterning,"
said Blatchford. "There are also some other tricks you can play with pitch
doubling, making it feasible to achieve 10-nanometer with immersion
lithography."

EUV is still being developed, and many
semiconductor houses have expressed a willingness to move to EUV when it
becomes available, but others are now predicting that immersion
lithography, multi-patterning and high-index fluids, will allow
semiconductors to make it all the way to the end of the International
Technology Roadmap for Semiconductors at eight-nanometer using
193-nanometer lithography.

"Its hard to say whether some
revolutionary new architecture will evolve that enables scaling of
silicon beyond the end of the current roadmap," said Blatchford. "But Intel
has publicly said that even if EUV never works, it will be able to make
immersion lithography work all the way to the end of the current
roadmap."

Nikon, Canon and ASML have all been hard at work
trying to make EUV work for almost a decade, since it uses light
wavelengths as short as 10-nanometer and thus theoretically could enable
sub-five nanometer features only a few molecules wide. However, by then
carbon-based electronics may start us down a new roadmap
altogether--one that discards lithography's subtractive masks, in favor
of additive self-assembly that begins with individual atoms from the
bottom-up.